During the formation of the lens, a transient vessel network, the hyaloid network, forms to nourish the lens as it develops. However, during late fetal development in humans and early postnatal development in mice, hyaloid vessels undergo regression to enable a transparent path of vision through the lens. Abnormal regression or growth of the hyaloid vasculature results in several diseases, including persistent hyperplastic tunica vasculosa lentis (PHTVL), persistent hyperplastic primary vitreous (PHPV), persistent fetal vasculature (PFV) and persistent prepupillary membrane (PPM). In this study, we will use fluorescent reporter mice labeling key cell types involved in vessel regression, live confocal imaging and FACS sorting and expression analysis to define cellular events leading to the onset of vessel regression. PUBLIC HEALTH RELEVANCE: The abnormal growth and regression of blood vessels in the eye is the leading cause of blindness in children, adults and the elderly (Campochiaro, 2000). This study will use vital imaging to characterize how vessels regress in the newborn eye using mouse models in which individual cell types in the hyaloid vasculature are labeled with fluorescent protein reporters. Live imaging and FACS sorting will be used to define novel events in that initiate vessel regression.